Electromagnetic product and process of making the same



Patented Sept. 16, 1946 ZAQZZM ELECTROMAGNETIC PRODUCT AND PROCESS OF ll/IAKING THE SAME Robert G. Guthrie and John Chumasero, Chicago,

111., assignors to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation'of Delaware No Drawing. Application May 31, 1941, Serial No. 396,180

2 Claims. 1

This invention relates to the production of devices having valuable magneticproperties, the compositions employed therein and to the processes for producing the compositions and devices. The invention also involves the production of such devices in a finished or substantially completed form by molding and sintering a mixture of powders which may consist of the elemental metals, carbonyl metal powders, alloys, or a mixture of such powders.

The invention further involves the process of producing powdered and sintered elements in the form and shape of completed devices or elements having valuable properties of a type which particularly adapt them for use as cores for electromagnetic armature actuating devices.

A further object of the invention is to provide a finished core element of a type employed in electromagnetic relays, while in some applications of the invention minimizing and in other applications of the invention eliminating entirely the necessity for the performance of relatively costly working and treating operations which in general also substantially affect the electromagnetic properties of the core. For example, a particular object of the invention is the elimination of difiicult machining, grinding, or stamping operations which seriously disrupt the magnetic properties of the core in-addition to being relatively costly. It is also an object of the invention to minimize the necessity for the performance of relatively costly working operations, both as to the extent and number of such operations as may be required. It is thus possible to effect a relatively very great reduction in the cost of producing completely finished elements of a type where working operations, such as machining or grinding, may not be wholly eliminated, or where sizing operations such as cold coining are desired to insure that the finished elements are produced to an exact size.

The manufacture of the finished core for electromagnetic armature actuating devices in the past was normally accomplished by thetreatm-ent of stock having, or by reason of proper treatment capable of acquiring, desired electromagnetic properties by performing thereon various operations such as forging, casting, bending, ma-

chining and grinding. The very generally rechanges in the. mechanical or physical condition of the. magnetic core material and also with changes in heat treatment or of the chemical composition. As a result of changesin the' mechanical or physical condition of the stock, further treatment as by annealing is usually neces-' sary in order to restore or embody in the struc-' ture of the core the required magnetic properties. It is especially noteworthy that necessary operations such as the machining, drilling, or grinding of the core members inorder to produce completed elements of the type employed in the magnetic core structure for relay devices, constitute difiicult and relatively very expensive op-v erations in addition to being detrimental to the magnetic properties of the stock.

In the past such articles as lamp filaments, gears and dies have been produced by compressing compositions of powdered materials into shape and sintering them. Also, devices having desirable .magnetic properties especially fitting them for use as permanent magnets, loading coils and devices adapted for use in communication fields have for some time been successfully produced from compressed and sintered compositions. Additional heating or working treatments are in general required in connection with these types of sinteredmagnetic devices. Molded inductance devices which employ Bakelite for bondingand for insulating the powdered elements also have been produced from powdered materials.

Sintered materials and elements produced in accordance with the present invention have val- I uable magnetic properties of the type generally employed in armature actuating devices, such as relays, but it is not intended to limit their application beyond the scope of the appended claims. The electromagnetic properties or" the materials produced in accordance with the invention comprise relatively high permeabilities, high values of fiux density, relatively very low coercive forces, low residual magnetism and relatively high saturation points. The physical struc ture of the sintered material discloses that the powdered elements have been difiused and bonded into relatively homogeneous forms.

One property of the permanent magnet type of device that readily causes it to distinguish over the material of the present invention is the high coercive force. Other devices previously produced from powdered metals which have low coercive force and high permeability values distinguishjgenerally from those produced in accordance with the invention by reason of having low flux densities, or low saturation points and relatively constant permeabilities. Certain of these electromagnetic devices are also distinguished over the present invention by reason of I having relatively very low resistivity and depend on their ability to operate on the application of extremely low or weak values of current. The well kIlOWn type of molded inductance device employing bakelite or other synthetic insulating and bonding material is of a non-homogeneous structure that is not productive of the higher permeabilities required for the relay type of core structure embodied in the present invention.

In the production of electromagnetic armature actuating core structures, it is found that in general impurities may be very harmful to the production of a material that is relatively homogeneous, or of one that possesses the desired lattice structure and magnetic properties. For example, carbon is very harmful even in the small percentages contained in commercially pure iron, although this may contain only as much as 0.4 to 0.5% of carbon. The commercially produced iron will also contain between 1% and 2% of oxygen which is undesirable together with traces of sulphur and phosphorous. Considerable caution must be exercised to assure that the metals embody a minimum of such impurities.

The powdering of an elemental metal and also the powdering and mixing of prealloyed metal stock is preferably carried out in ball mills, although other known types of powdering mills may be employed, and wherein the treatment i continued until the metal is sufficiently commi nuted to conform to the desired sieve analysis A lubricant, preferably of a volatile type, may be added to the powders to assist in the pressing and molding operation. When in this manner an alloy is powdered each metal grain of this powde1 is in itself an alloy and may be defined as a prealloyed powder.

The mixing of the powders in preparation for the cold pressing and molding operation in accordance with the series of processes embodied in the invention may be accomplished in various manners well known in the art. We find it preferable to employ powder of a size such that all will pass through a 200 mesh sieve and in addition to which 80 to 85% of this quantity will pass through a 325 mesh sieve. A small percentage of lubricant varying in amount from 0.5% to 1% and preferably of a volatile type may be mixed with the powders in order to facilitate the pressing and molding operation. A lubricant of known form such as paraffin, petroleum jelly, or stearic acid may be employed.

The molding operation may be performed by the application of large pressures and a fairly wide range of pressures may be employed. In forming the material to a desired finished shape, great accuracy and the elimination of waistline effects may be secured by the use of theproper lubrication and the proper pressures. In most of the series of processes described below, it is found that the addition of 0.5 to 1% of a lubricant which is preferably of a volatile type and the use of pressures of to tons per square inch are productive of highly satisfactory molding operations. The molding pressures which are cited have particular reference to the formation of cores for electromagnetic relays. Where a volatile lubricant has been employed in the molding operation, it may be found desirable to submit the molded device to a baking operation at a temperature sufiicient to volatilize and eliminate the lubricant.

The sintering, or combined sintering and annealing operations, are of great importance with 5, reference to the provision of commercially practicable methods of production and are likewise of a fairly critical nature. In the examples of the invention described below, it may be noted that, in general, sintering temperatures having a range of from 2000 F. to 2350 F. are employed together with sintering times of from two to twelve hours. The duration of the sintering operation may be varied considerably but must be sufficient to permit the material to properly diffuse and consolidate for'forming the relatively homogeneous composition from which the valued electromagnetic properties are obtained. The variation in permissible sintering times is found to vary in accordance with the temperature employed. The sintering is preferably carried out in a non-oxidizing atmosphere or reducing gas such as hydrogen in accordance with known practices.

The molded devices when sintered have incorporated therein the valued magnetic properties. However, in accordance with certain methods for producing the devices commercially, or Where the elements must be held to very close dimensional requirements, it may be desirable to subject the sintered element to a sizing operation such as a cold coining, pressing, or other known treatment as a step immediately following he sintering operation. Also, while the necessity of performing such operations as machining or shaping will in most cases be eliminated, it may be desired to construct a sintered device of such form and shape that although machining or other operations are reduced toa minimum some working operations are necessary. sintered devices of this nature which because of the particular Way of producing them commercially are subjected to mechanical strain, or which may for some reason require the performance of machining, sizing, or other working operations thereon will, in general, then be treated to restore the desired magnetic properties therein. The preferred treatment is to anneal such devices in a nonoxidizing atmosphere such as hydrogen and at temperatures similar to those employed in the direct sintering operation. The annealing opera- 50 tion is of relatively short duration compared to the sintering period. In the examples given below the annealing may be accomplished in a period of from forty-five minutes to one hour.

An electromagnetic relay core, of a type which in particular may be constructed in accordance with our invention, may consist of a simple rectangular shaped solid having a slot across one end thereof and a centrall tapped portion, adapted to receive a screw for securing the core to the relay structure, in the other end thereof. A major reduction in the cost of the production of a relay core of this type may readily be effected by the production thereof in accordance with'our invention.

The invention will be more fully understood by reference to the below described examples for producing thesintered magnetic elements. In general, the sintered elements of the desired shape preferably comprise from 45 to 55% of iron and 70 from 45 to 55% of nickel in substantially equal amounts, but in addition may include from 1 to 10% of one or more of the metal group consisting of tin, molybdenum and chromium in keeping with certain of the processes described below.

In accordance with one form of our invention for producing the sintered device, carbonyl metal powders or carbonyl metal, powder andanv ele mental metal powder are mixedto obtain the proper proportions of the nickel and iron metals from which the desired magnetic properties are obtained and Without requiring the addition of other elements for'bonding or purifying purposes. That carbonyl metal powders may be so employed is believed possible largely because of the existence therein of but relatively very small percentages of harmful impurities. This application. of carbonyl metal powders to the production of completely formed and shapedsintered elements having .very desirable magnetic propertie and requiring no additional metal working and treating or of such elements while requiring a minimum of relatively costly working operations constitutes any important feature of the invention.

As an example of this form of the invention, a mixture of powdered carbonyl iron and powdered nickel in approximately equal percentages of iron and nickel when pressed and molded at a pressure of 40 tons per square inch and sintered for fifteen hours at a temperature of 2250 F. in a non-oxidizing atmosphere of hydrogen is productive of a material having the following properties. .Should working operations be required in connection with the sintered device, or be performed in connection with certain methods for commercially handling the sintered devices, an annealing operation under conditions similar to those employed in sintering but extending for a period offrom forty-five minutes to one hour would be employed.

Initial permeability 2,760 Maximum permeability 10,150 Ho (oersteds) L 1 0.156 Br (gausses) 1,098

Another example of this form of the invention consists in the use of the elemental powders of iron and nickel in substantially equal amounts and containing a minimum of impurities. The elemental iron powder employed contains 0.015% carbon, 0.012% sulphur and 1.5% oxygen. The nickel contains 0.6%to' 0.7% cobalt, traces of iron, carbon, silicon dioxide, and about 2% oxygen. This composition when sintered for twenty-five hours at 2175 F. in a reducing atmosphere of hydrogen produced the following results:

Initial permeability 1065 Maximum permeability 9060 He (oersteds) 0.31 Br (gausses) 2520 In View of the results obtained it appears that the sintering treatment, although of an extremely long duration, successfully removed from or minimized the harmful impurities contained in the molded composition. Thus, by sintering in a reducing atmosphere of hydrogen the hydrogen reacts with iron oxide to reduce it to iron, also with iron carbide to reduce it to iron and with iron sulphide to reduce that to iron. The result of the sintering operation is to eliminate or reduce to a minimum the harmful effects of the impurities in addition to diffusing and bonding the composition into a structure of the relatively homogeneous type embodying the magnetic properties.

In accordance with a second form of the invention for producing sintered magnetic devices, powders of the elemental metals from which the desired magnetic properties are primarily obtained are employed and additional powdered employing a powdered composition containing from 40 to 60% of iron, from 40 to 60% of, nickel and from 2 to 10% of one or more of the metals of the group consisting of tin, molybdenum and chromium. This method may, for example, be performed by the use of 90 to 98% of nickel and iron powders in substantially equal amounts and from 2 to 10% of chromium or molybdenum. Very favorable results are obtained by a composition of elemental metal powders having the following pro-portions: iron 48.79%, nickel 48.79%, molybdenum 2.42% and small residual amounts of carbon, silicon and manganese. A molding pressure of 40 to 50 tons per square inch is employed. The devices. are sintered in a reducing atmosphere of hydrogen for twelve hours at a temperature of 2200 F., and where required, an annealing operation of three quarters of an hour to one hour at 2250 F. may be employed. The magnetic properties produced in the material are;

Initial permeability flu; 2,560

Maximum permeability 10,200 Ho (oersteds)..." 0.207 Br (gausses) 11,957

Initial permeability 4,280 Maximum permeability 10,500 Hc (oersteds) 0.206 Br (gausses) 1,965

The following results are obtained by a composition comprising: iron 47%, nickel 47%, chromium 2% and tin 4% wherein the material is molded at a pressure of 50 tons per square inch and sintered in a hydrogen atmosphere for fiv hours at 2350 F.

Initial permeability 3,520 Maximum permeability 20,450 Hc (oersteds) 0.184 Br (gausses) 990 In employing this composition successful results are secured although the commercially produced iron powder may contain as much as 0.5% of carbon. It is believed that this relatively high percentage of carbon and other impurities may be employed as a result of the addition of the powders of the molybdenum, chromium, and tin series. For example, the normally harmful properties of the tin are believed to be more than offset by the absorption, purifying and alloying 7 action which this metal appears to exert on the carbon and other impurities contained in the constituent metals.

The third and preferred form of our invention for producing the sintered devices of desired shape and from which excellent magnetic properties are obtained embodies the use of prealloyed powders. In th practice of this method it is preferred to first produce or employ a metal alloy having the exact composition of the desired magnetic sintered device. This metal alloy stock is reduced to powdered form in any Well known manner, but preferably ina ball mill operated in the manner described above. Each grain of the alloyed powder is in this case an alloy having the composition of the ultimately produced device. Although the practice is not preferred, small additions of other powdered alloys or of powdered elemental metals may be added to the primary prealloyed powder in order to secure a desired composition difiering from that contained in the primary prealloyed powder.

When the prealloyed powders are employed and each grain of the powder is an alloy having the exact composition desired, the molding and sintering operations serve merely to diffuse and bond the material into a relatively homogeneous article of the desired shape and size, since any alloying efiect which might otherwise be required is eliminated, or .in any event, reduced to a minimum.

In this preferred form of our invention, an alloy may be employed having a composition embraced in the methods and examples described above, except possibly for the use of tin which may not readily be combined to form such alloys. A powdered alloy containing 47.4 to 47.8% nickel, 2.25 to 2.78% molybdenum and the balance of iron, except for small residual amounts of ca;- bon, silicon and manganese may well be employed in producing the electromagnetic relay core devices. The limits expressed in connection with this composition are not critical and merely constitute an analysis of a particularly desirable composition. This magnetic material may be sintered in a hydrogen atmosphere at a temper- 8 ature of only 2200 F. and extending for a period of but five hours. The magnetic properties of the sintered device are:

Initial permeability 2,500 Maximum permeability 18,700 Hc (oersteds) 0.184 Br (gausses) 3,294

Compositions of prealloyed powder that might be recommended include nickel-iron alloys employing to of nickel and embracing a composition such as 50% of iron, 49% nickel,

0.60% manganese, and 0.20% silicon.

The examples of the invention disclosed above are intended to be merely illustrative. Other variations and applications of the invention will readily occur to those skilled in. the art. Therefore, our invention should be no more limited than as determined in accordance with the appended claims.

We claim as our invention:

1. A method for producing a high permeability sintered core structurefor an electromagnet with a minimum of further metal working being required which comprises employing material in powdered form, the composition of said powder substantially comprising equal portions of iron and nickel and 2 to 3 per cent of the group consisting of molybdenum and chromium, molding the powdered material to the desired shape, and sintering the same by the application of pressure and heat until the saturation point is high, the initial permeability is over 2,000, the maximum permeability is over 10,000, the coercive force is less than 0.250 oersted, and the residual flux density is less than 4,000 gausses.

2. A sintered magnetic core containing 47 to 49 percent of nickel, 2.25 to 2.78 percent of molybdenum, and substantially the entire balance of iron, said core having a high saturation point, an initial permeability of over 2,000, a maximum permeability of over 10,000, a coercive force of less than 0.250 oersted, and a residual flux density of less than 4,000 gausses.

ROBERT G. GUTHRIE. JOHN CI-IUMASERO. 

